diff --git a/embedded-workshop-book/src/setup-stage.md b/embedded-workshop-book/src/setup-stage.md index a301a30..7e1303d 100644 --- a/embedded-workshop-book/src/setup-stage.md +++ b/embedded-workshop-book/src/setup-stage.md @@ -7,24 +7,32 @@ In `usb-2.rs`, you will find a short description of each register above the vari [nrf product spec]: https://infocenter.nordicsemi.com/pdf/nRF52840_PS_v1.1.pdf +## Writing a parser for the data of this SETUP stage. + +❗️ Keep the cable connected to the J3 port for the rest of the workshop + +✅ Parse GET_DESCRIPTOR requests for DEVICE descriptors. + +Modify `Request::parse()` in `advanced/common/usb/src/lib.rs` to recognize a GET_DESCRIPTOR request of type DEVICE so that the `get_descriptor_device` test passes. Note that the parser already handles SET_ADDRESS requests. + +**Getting Started:** + +**1. Writing code that can be tested** + When you need to write some `no_std` code that does not involve device-specific I/O you should consider writing it as a separate crate. This way, you can test it on your development machine (e.g. `x86_64`) using the standard `cargo test` functionality. So that's what we'll do here. In `advanced/common/usb/lib.rs` you'll find starter code for writing a `no_std` SETUP data parser. The starter code contains some unit tests; you can run them with `cargo test` (from within the `usb` folder) or you can use Rust Analyzer's "Test" button in VS code. The definition of `Descriptor::Configuration` as well as the associated test has been "commented out" using an `#[cfg(TODO)]` attribute because it is not handled by the firmware yet. Delete the `#[cfg(TODO)]` so that the unit tests can access it. This pattern is used for enum members and test functions throughout this workshop, so keep it in mind should you see it again. -✅ Parse the data of this SETUP stage. - -❗️ Keep the cable connected to the J3 port for the rest of the workshop - -Start with the GET_DESCRIPTOR request, which is described in detail in section 9.4.3 of the [USB specification][usb_spec]. All the constants we'll be using are also described in Tables 9-3, 9-4 and 9-5 of the same document. - -[usb_spec]: https://www.usb.org/document-library/usb-20-specification +**2. Description of GET_DESCRIPTOR request** We can recognize a GET_DESCRIPTOR request by the following properties: - `bmRequestType` is **0b10000000** - `bRequest` is **6** (i.e. the GET_DESCRIPTOR Request Code, defined in table 9-4 in the USB spec) + +**3. Description of DEVICE descriptor requests** In this task, we only want to parse DEVICE descriptor requests. They have the following properties: - the descriptor type is **1** (i.e. DEVICE, defined in table 9-5 of the USB spec) @@ -32,29 +40,33 @@ In this task, we only want to parse DEVICE descriptor requests. They have the fo - the wIndex is **0** for our purposes - ❗️you need to fetch the descriptor type from the high byte of `wValue`, and the descriptor index from the the low byte of `wValue` +Check section 9.4.3 of the [USB specification][usb_spec] for a very detailed description of the requests. All the constants we'll be using are also described in Tables 9-3, 9-4 and 9-5 of the same document. + +**4. Remember that you can define binary literals by prefixing them with `0b`.** + +**5. You can use bit shifts (`>>`) and casts (`as u8`) to get the high/low bytes of `wValue`.** + +**6. Return `Err` if properties aren't met.** + You will also find this information in the `// TODO implement ...` comment in the `Request::parse()` function of `lib.rs` file. > NOTE: If you'd like to learn more, take a look at Section 9.4.3 Get Descriptor of the USB specification. -To complete the task, proceed like this: - -1. **Parse GET_DESCRIPTOR requests for DEVICE descriptors:** -Modify `Request::parse()` in `advanced/common/usb/src/lib.rs` to recognize a GET_DESCRIPTOR request of type DEVICE so that the `get_descriptor_device` test passes. Note that the parser already handles SET_ADDRESS requests. - - - remember the GET_DESCRIPTOR fields described at the start of this section - - remember that you can define binary literals by prefixing them with `0b` - - you can use bit shifts (`>>`) and casts (`as u8`) to get the high/low bytes of `wValue` - See `advanced/common/usb/solution-get-descriptor-device.rs` for a solution. -2. **Read incoming request information and pass it to the parser:** -modify `usb-2.rs` to read `USBD` registers and parse the SETUP data when an EPSETUP event is received. +✅ Read incoming request information and pass it to the parser: + +modify `usb-2.rs` to read `USBD` registers and parse the SETUP data when an EP0SETUP event is received. + +**Getting Started:** + - for a mapping of register names to the `USBD` API, check the entry for `nrf52840_hal::target::usbd` in the documentation you've created using `cargo doc` - - remember that we've learned how to read registers in `events.rs` + - let bmrequesttype = usbd.bmrequesttype.read().bits() as u8; + - remember that we've learned how to read registers in `events.rs`. - you will need to put together the higher and lower bits of `wlength`, `windex` and `wvalue` to get the whole field - > Note: If you're using a Mac, you need to catch `SetAddress` requests returned by the parser as these are sent before the first GetDescriptor request. You can handle them by doing nothing. -3. when you have successfully received a GET_DESCRIPTOR request for a Device descriptor you are done. You should see an output like this: +1. when you have successfully received a GET_DESCRIPTOR request for a Device descriptor you are done. You should see an output like this: ``` console INFO:usb_2 -- USB: UsbReset @ 438.842772ms @@ -67,5 +79,7 @@ INFO:usb_2 -- Goal reached; move to the next section `wlength` / `length` can vary depending on the OS, USB port (USB 2.0 vs USB 3.0) or the presence of a USB hub so you may see a different value. -You can find a solution to step 1. in `advanced/common/usb/solution-get-descriptor-device.rs`. -You can find a solution to step 2. in `advanced/firmware/src/bin/usb-2-solution.rs`. + +You can find a solution to this step in `advanced/firmware/src/bin/usb-2-solution.rs`. + +[usb_spec]: https://www.usb.org/document-library/usb-20-specification